Biopsy needles are generally classified as being either an end cutting needle, commonly referred to as a "Menghini needle" or, a side cutting needle such as the type generally known as "Tru-cut" needles. The present invention was specifically developed as an improvement to the Tru-cut needle, but, as discussed hereafter, can also be used as an end cutting needle.
Generally, an end cutting needle includes a hollow cannula having an especially configured, circumferentially sharpened, open end at its distal portion. A stylet is conventionally inserted into the hollow shaft of the cannula and extends flush with the open cutting edge of the cannula to close the open end. The biopsy needle is then inserted and the stylet functions to puncture the site of the lesion where the biopsy specimen is to be taken. The stylet is then withdrawn and the cannula further inserted into the lesion with the result that the tissue is cut and fills the now open cutting end of the cannula. A suction device is typically applied to a proximal portion of the cannula to withdraw the tissue sample thus taken. Alternatively, the cannula can be rotated to sever the tissue and then withdrawn from the site. Reference should be had to my '147 patent and particularly FIGS. 7-13 thereof which show prior art, end cut needles.
In the side cut needle, there is a "solid" inner cannula within an outer cannula and the inner cannula generally has a leveled, circumferentially sharpened distal end shaped to a pointed end with a cutting groove or tissue gap formed at the distal portion of the inner cannula behind the pointed end. The side cut needle advances to the site where the lesion is to be extracted and is rotated so that the cutting groove severs the tissue. The outer cannula advances over the inner cannula to encapsulate the specimen there between. Alternatively, the outer cannula can have a cutting edge formed about its opening and simply be advanced over the tissue gap space to cut the lesion or biopsy specimen thus trapping the specimen within the gap.
The most widely used cutting and puncturing tip of a biopsy needle is simply that of a beveled tip which is circumferentially and axially sharpened to a point. The bevel lies in a plane which forms an acute angel with the longitudinal center line of the cannula, typically anywhere from 20.degree. to 45.degree.. Conical pointed ends have also been used to puncture the site. (See for example FIG. 4a and FIG. 11 of my '174 patent.) Technically, conical pointed needle tips do not cut the tissue nor do they have a mechanism to prevent deviation. They merely puncture the site. The circumferentially sharpened end of the cannula is used to cut the lesion.
As noted in my prior patents, complications can arise from the use of biopsy needles while positioning the needle and while severing the specimens to be taken. To accurately guide the biopsy needle, percutaneous procedures have been developed which permit visual radiological observation of the instrument inside the body. In fact, biopsy needles have been developed with a configuration to provide good images in conjunction with CT guided biopsies. Also, better CT scanning images have been developed as the scanning art has advanced which enable the entire distal portion of the needle to be accurately positioned within the site where the biopsy specimen is to be extracted.
Nevertheless, it should be understood that the characteristics of lesion tissue vary and in some instances may be determinable only during the biopsy procedure. While some tissue is resilient, other tissue may be hard and resistant to penetration. Specifically in biopsies of the breast, the tumors or lesions are often small, hard masses. When the needle tries to penetrate or puncture the tumor, the needle tip will actually deflect before the tumor is punctured. Often the tumor will move when the needle tip deflects making extraction of the specimen difficult or impossible. Sometimes fracture of the tumor will occur when the needle deflects causing complications.
Conceptually, there are other procedures where body organs or parts, even bone, have to be accessed to withdraw a specimen by penetrating rigid matter. In these "hard applications" in which access is to be provided by a needle, the needle tip, especially the beveled tip (but also the cone shaped tip) deflects during the puncture/cutting/insertion portion of the procedure. The deflection prevents accurate positioning of the needle.